Marine food web

In Antarctica, light is the most important environmental factor affecting marine organisms. Without it, plants that are the base of all food chains cannot grow.
The most important plants in the Southern Ocean are tiny algae called phytoplankton.
The main types of algae are diatoms and dinoflagellates.
Further south, the ice algae that grow under and within pack ice and snow are also important.
Algae grow well in Antarctic waters because of a plentiful supply of nutrients brought to the surface by upwelling warmer water.
Krill, small animals that feed on phytoplankton, dominate the zooplankton.
There are about 600 000 billion krill in the Southern Ocean, weighing 500 million tonnes. They are the most abundant animal in the world.
It is estimated seabirds eat more than 115 million tonnes of krill per year.
The Antarctic food web is very sensitive to change. Any change in the numbers of one species is likely to have major impacts on others.
Crabeater seals outnumber all other seals in the world put together.

Humans currently harvest about 100 000 tonnes of krill per year, mostly in the same convenient locations used by seals and penguins. Dried krill are close to 50% protein and rich in vitamins, so this harvest can be expected to increase.
Humans catch large numbers of Patagonian and Antarctic toothfish, and there is a danger this fishery could be over-exploited. (Only 120 of the 20 000 known species of fish live south of the Antarctic Convergence.)
Long-line fishing kills more than 100 000 seabirds a year.